5Interpreting the signalSize and depthvisual angle indicates how much of view object occupies (relates to size and distance from eye)visual acuity is ability to perceive detail (limited)familiar objects perceived as constant size (in spite of changes in visual angle when far away)cues like overlapping help perception of size and depth

6Interpreting the signal (cont)Brightnesssubjective reaction to levels of lightaffected by luminance of objectmeasured by just noticeable differencevisual acuity increases with luminance as does flickerColourmade up of hue, intensity, saturationcones sensitive to colour wavelengthsblue acuity is lowest8% males and 1% females colour blind

7Interpreting the signal (cont)The visual system compensates for:movementchanges in luminance.Context is used to resolve ambiguityOptical illusions sometimes occur due to over compensation

11Hearing (cont) Humans can hear frequencies from 20Hz to 15kHzless accurate distinguishing high frequencies than low.Auditory system filters soundscan attend to sounds over background noise.for example, the cocktail party phenomenon.

12Touch Provides important feedback about environment.May be key sense for someone who is visually impaired.Stimulus received via receptors in the skin:thermoreceptors – heat and coldnociceptors – painmechanoreceptors – pressure (some instant, some continuous)Some areas more sensitive than others e.g. fingers.Kinethesis - awareness of body positionaffects comfort and performance.

13MovementTime taken to respond to stimulus: reaction time + movement timeMovement time dependent on age, fitness etc.Reaction time - dependent on stimulus type:visual ~ 200msauditory ~ 150 mspain ~ 700msIncreasing reaction time decreases accuracy in the unskilled operator but not in the skilled operator.

14Movement (cont)Fitts' Law describes the time taken to hit a screen target:Mt = a + b log2(D/S + 1)where: a and b are empirically determined constantsMt is movement timeD is DistanceS is Size of targettargets as large as possible distances as small as possible

15Memory There are three types of memory function: Sensory memoriesShort-term memory or working memoryLong-term memorySelection of stimuli governed by level of arousal.AttentionRehearsal

23Script for a visit to the vetModels of LTM - ScriptsModel of stereotypical information required to interpret situationScript has elements that can be instantiated with values for contextScript for a visit to the vetEntry conditions: dog illvet openowner has moneyResult: dog betterowner poorervet richerProps: examination tablemedicineinstrumentsRoles: vet examinesdiagnosestreatsowner brings dog inpaystakes dog outScenes: arriving at receptionwaiting in roomexaminationpayingTracks: dog needs medicinedog needs operation

24Models of LTM - Production rulesRepresentation of procedural knowledge.Condition/action rulesif condition is matchedthen use rule to determine action.IF dog is wagging tailTHEN pat dogIF dog is growlingTHEN run away

25LTM - Storage of informationrehearsalinformation moves from STM to LTMtotal time hypothesisamount retained proportional to rehearsal timedistribution of practice effectoptimized by spreading learning over timestructure, meaning and familiarityinformation easier to remember

26LTM - Forgetting decay interferenceinformation is lost gradually but very slowlyinterferencenew information replaces old: retroactive interferenceold may interfere with new: proactive inhibitionso may not forget at all memory is selective …… affected by emotion – can subconsciously `choose' to forget

27LTM - retrieval recall recognitioninformation reproduced from memory can be assisted by cues, e.g. categories, imageryrecognitioninformation gives knowledge that it has been seen beforeless complex than recall - information is cue

29Deductive Reasoning Deduction:derive logically necessary conclusion from given premises.e.g. If it is Friday then she will go to workIt is FridayTherefore she will go to work.Logical conclusion not necessarily true:e.g. If it is raining then the ground is dryIt is rainingTherefore the ground is dry

30Deduction (cont.) When truth and logical validity clash … Correct?e.g. Some people are babiesSome babies cryInference - Some people cryCorrect?People bring world knowledge to bear

31Inductive Reasoning Induction: Unreliable: … but useful!generalize from cases seen to cases unseene.g. all elephants we have seen have trunks therefore all elephants have trunks.Unreliable:can only prove false not true… but useful!Humans not good at using negative evidencee.g. Wason's cards.

32How many cards do you need to turn over to find out?Wason's cards7 E 4 KIf a card has a vowel on one side it has an even number on the otherIs this true?How many cards do you need to turn over to find out?…. and which cards?

34Problem solvingProcess of finding solution to unfamiliar task using knowledge.Several theories.Gestaltproblem solving both productive and reproductiveproductive draws on insight and restructuring of problemattractive but not enough evidence to explain `insight' etc.move away from behaviourism and led towards information processing theories

36Problem solving (cont.)Analogyanalogical mapping:novel problems in new domain?use knowledge of similar problem from similar domainanalogical mapping difficult if domains are semantically differentSkill acquisitionskilled activity characterized by chunkinglot of information is chunked to optimize STMconceptual rather than superficial grouping of problemsinformation is structured more effectively

38Emotion Various theories of how emotion worksJames-Lange: emotion is our interpretation of a physiological response to a stimuliCannon: emotion is a psychological response to a stimuliSchacter-Singer: emotion is the result of our evaluation of our physiological responses, in the light of the whole situation we are inEmotion clearly involves both cognitive and physical responses to stimuli

39Emotion (cont.)The biological response to physical stimuli is called affectAffect influences how we respond to situationspositive  creative problem solvingnegative  narrow thinking“Negative affect can make it harder to do even easy tasks; positive affect can make it easier to do difficult tasks”(Donald Norman)

40Emotion (cont.) Implications for interface designstress will increase the difficulty of problem solvingrelaxed users will be more forgiving of shortcomings in designaesthetically pleasing and rewarding interfaces will increase positive affect

42Psychology and the Design of Interactive SystemSome direct applicationse.g. blue acuity is poor  blue should not be used for important detailHowever, correct application generally requires understanding of context in psychology, and an understanding of particular experimental conditionsA lot of knowledge has been distilled inguidelines (chap 7)cognitive models (chap 12)experimental and analytic evaluation techniques (chap 9)